Traveling wave electron discharge devices



July 22, 1958 E. c. DENCH TRAVELING WAVE ELECTRON DISCHARGE DEVICES Filed Oct. 23. 1953 W n my M United States Patent TRAVELING WAVE ELECTRON DISCHARGE DEVICES Edward C. Dench, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application October 23, 1953, Serial No. 387,968

16 Claims. (Cl. 332-25) This invention relates to a traveling wave type electron discharge device and more particularly to a frequency modulated oscillator of the traveling wave type. A carcinotron or backward wave oscillator of the traveling wave type is discussed in an application for United States Letters Patent of E. C. Dench, Serial No. 382,024, filed September 24, 1953, which includes a periodic anode delay network, a continuous negative electrode or sole spaced from and disposed substantially parallel to the anode network, and an electron source for producing an electron beam which traverses the interaction space between anode and sole. The sole is preferably made in the form of a channel having a major surface parallel to the anode and vertical walls at each edge of the electrode which approach or slightly overlap the anode network. The vertical Walls serve as a beam forming end shield and keep the electron stream centered in the system and from diverging in a direction normal to the path of the electrons owing to mutual repulsion of the space charge along the length of the tube.

The velocity of the backward component of a traveling wave in periodically loaded microwave networks, such as strapped vane structures, interdigital arrays and the like, varies with frequency. As the velocity of the electron beam is varied, substantial synchronism is obtained with the phase velocity of a backward component of the traveling wave for a given frequency, and oscillations will occur within the tube.

The average velocity of the electron beam is dependent upon the intensity E of the electric field between anode and sole and upon the strength B of the transverse magnetic field and is equal to the ratio If the spacing d between anode and sole and the magnetic field strength are fixed, the average velocity of the electron beam is dependent only upon the strength of the electric field. By varying the strength of the electric field, the beam velocity may be varied with a resulting variation in frequency of the traveling wave oscillator. If the anode network and negative electrode are supplied by separate sources whose voltages with respect to a common reference point, such as the cathode, are +V and V respectively, the electric field E may be given y The electric field obviously may be altered by varying either the positive anode voltage V or the negative electrode voltage V in order to tune the oscillator. It has been found that a greater tuning range is possible by variation of the voltage V than is possible by variation of the negative electrode voltage V Because of the comparatively heavy current in the anode relative to that in the sole, however, the power requirements for frequency modulation using anode voltage tuning are greater than those using sole voltage tuning.

If only a small amount of tuning is adequate, it can be achieved by varying the potential of the negative electrode. This method of tuning is superior to anode tuning in that the current may be of the order of only oneeighth that of the anode.

This method, however, is inadequate for applications in which it is desired to modulate the sole potential at a high rate of the order of five to ten megacycles, since the relatively large negative electrode presents considerable capacitance.

As stated before, the sole is so constructed as to exert the proper forming and focusing of the electron beam and is slightly wider than the transverse dimensions of the anode network or electron beam. The major portion of the sole is spaced relatively close to the anode inasmuch as the strength of the electric field produced between the anode and sole is inversely proportional to the distance therebetween. Moreover, the spacing between anode and sole is likely to be a minimum in the region of the tips of the vertical walls of the sole where the sole overlaps the anode. Because of the relatively large size of the sole and its proximity to the anode, the capacitance between anode and sole is quite large. This large capacitance is of no concern in so far as the unidirectional field producing means is concerned, but is not permissible for operation at frequencies of the order of from Zero to five or ten megacycles, since the capacitive reactance shunting the modulating voltage source at those frequencies becomes so low that the power rating of the modulator necessary to produce the desired modulation of the electric field over a band of frequencies becomes prohibitive.

In accordance with this invention, the capacitance between the tube electrodes across which the modulator is connected and, consequently, the power requirement of the modulator, is substantially reduced by providing an auxiliary electrode, preferably in the form of a wire or thin strip, which cooperates with the sole for varying the oscillator frequency. This auxiliary electrode is positioned adjacent the sole and is centrally located with respect to the transverse dimensions of the tube so as to be in the region of most effective interaction between the electron beam and the traveling wave. This auxiliary electrode is relatively small compared with the sole and, unlike the sole, all portions of the auxiliary electrode may be spaced a considerable distance from the anode. The modulating voltage, in accordance with this invention, is connected between the auxiliary electrode and the anode.

The electron beam in most traveling wave tubes is confined approximately to the central transverse region of the tube. It is in this central region that the most effective interaction occurs between the electron beam and the R. F. field along the anode network. This is particularly true in a traveling Wave tube using an interdigital' anode network inasmuch as the R. F. distribution is a maximum at the center of the tube and a minimum at the side walls. For purposes of modulating the electric field between electrodes, therefore, a large negative electrode is superfluous. Moreover, the variation in intensity of the electric field necessary to frequency modulate the microwave traveling Wave tube Over a relatively narrow band is relatively small compared with that required for the mean operating frequency. For example, the oscillator may be varied about a mean frequency of 2000 megacycles at a ten-megacycle rate. A centrally located auxiliary electrode of relatively small surface area, therefore, is quite adequate in achieving the necessary modulations of the electric field.

By reducing the capacity shunted across the FM modulator, modulation at microwave frequencies may be ef-' 3 fected with less driving power and, consequently, with a substantial saving in cost, size and weight of modulating equipment.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference 'being bad to the accompanying drawings wherein:

Fig. 1 is a central longitudinal cross-sectional view of a traveling wave oscillator in accordance with the invention;

Fig. 2 is transverse cross-sectional view of the traveling wave oscillator of Fig. 1 taken along line 22 of Pi 1;

Fig. 3 is a fragmentary isometric view showing the relation between the auxiliary electrode and the sole of the tube of Figs. 1 and 2;

Fig. 4 is a schematic diagram of the electric field producing means for the tube of Fig. 1;

Fig. 5 shows the modification of the circuitry of Fig.

Fig. 6 is a fragmentary isometric view of a modification of the auxiliary electrode-sole assembly of Fig. 3; and

Fig. 7 illustrates a further modification of an auxiliary electrode-sole assembly.

A traveling wave tube 10 is shown in Fig. l which comprises a periodic anode structure 11, a cathode or electron source 12, a negative electrode or sole 13 arranged parallel to and spaced from the anode network 11, a positive collector electrode 14 at the end of the tube opposite from said cathode from collecting electrons not captured by the anode, an auxiliary modulating electrode 15 positioned adjacent said sole, and explained in more detail subsequently, an R. F. output coupling means 16 at the cathode end of the tube, and means including a pair of pole pieces 1.7 and 17 for producing a mag netic field transverse to the direction of motion of said electron beam.

The periodic anode network shown in Fig. l is of the type illustrated and described in a copending application for U. S. Letters Patent of E. C. Dench, Serial No. 382,133, filed September 24, 1953, and includes a base 19 forming one of the walls of an evacuated envelope further including an oppositely disposed wall 20, end walls 21 and 22, and a pair of side walls 23 and 24, shown in Fig. 2. The electrically conductive base 19 of anode 11 may be secured to contiguous walls of the envelope by brazing or by means of any appropriate fastening device. Base 19 contains. a plurality of spaced U-shaped loops 25 longitudinally disposed along base 19 and shorted at the ends by said base. of each loop may be brazed directly to the surface of the base, as shown in Fig. l, or may be inserted in oppositely disposed apertures in said base. A pair of spaced straps 26 and 27 are located near the center of each loop and are attached to alternately arranged loops,

as shown in Fig. 1.

It should be understood that the traveling wave tube according to this invention is not limited to one using a periodic anode structure of the type shown and described. The periodic anode delay network may take several forms, such as an interdigital line, a strapped solid vane structure or a disk loaded coaxial network.

Microwave energy is withdrawn from the tube by means of a coaxial output coupling device 16 having an outer conductor 29 connected to the tube envelope and an inner conductor 30 which extends through an aperture 31 in wall 19 and is attached, as by brazing, to one end of the first loop at the output end of the anode network.

A cathode structure 12 having an electron emissive surface 33 is positioned at the output end of the tube adjacent the anode. The cathode is supported by a hollow supporting cylinder 34 extending through an aperture in wall 20 of the tube envelope. Cylinder 34 surrounds a central conductor 35' which is connected to The ends one end of a heater coil (not shown) positioned in thermal proximity to cathode emissive surface 33. The details of this cathode are set forth in an application for U. S. Letters Patent of E. C. Dench, Serial No. 255,499, filed November 8, 1951, now Patent No. 2,809,328, dated October 8, 1957.

An electrode 13 is positioned substantially parallel to the anode network and spaced therefrom, as shown in Fig. 1. This electrode, which is maintained negative with respect to the anode, is often referred to as a sole. This electrode is constructed in the form of a channel whose base portion 13a is spaced uniformly from said anode network by a distance d. The sole, in conjunc-- tion with the anode, serves to maintain an electric field between the anode and sole along the length of the tube. The channel-shaped electrode 13 also includes a pair of oppositely disposed vertical side walls 13b extending upwardly from the edges of base portion 13a. These side walls approach or slightly overlap the anode structure and serve to keep the electron stream centered in the tube and keep it from diverging in the transverse direction owing to mutual repulsion of the space charge along the length of the tube.

Sole 13 is supported relative to the tube envelope by means of a support assembly 37 including a supporting rod 38 and by means of a supporting rod 38; both rigidly attached to the base of the sole. One of these rods 38 is insulatedly supported with respect to wall 20 by means of a metallic member 39 sealed in turn to ceramic seal 40. The latter is connected to an electrically conductive cylinder 41 which surrounds rod 38 and is, in turn, attached to a recess in wall 20 surrounding the aperture through which rod 38 passes. An electrical lead 42 connected external to the tube extends through the members 38 to 41 and is connected to sole 13. Since only one circuit connection need be made to the sole, the other supporting rod 38 may be of simpler construction, as, for example, a short cylindrical rod made of an electrically insulating material attached directly to the inner surface of wall 20.

A unidirectional electric field of intensity E is established between the anode and sole by connecting a source of D. C. voltage 50 therebetween, as shown schematically in Fig. 4. A transverse magnetic field is produced in the space between the periodic anode structure and the sole in a direction normal to the electric field. A portion of the pole pieces 17 and 17' is shown in Fig. 2; these pole pieces lie adjacent the side walls 23 and 24, respectively, of the tube envelope. By proper adjustment of the magnetic field, the electrons emitted from the cathode may be directed along a path adjacent the loops of the anode structure where effective interaction between the electron beam and the wave traversing the anode may be obtained.

The cathode is negative relative to the anode and may or may not be at the same potentials as the sole. In one application the cathode is somewhat more positive than the sole. See Fig. 5.

Positioned beyond the end of sole 13, remote from the output, there is a collector electrode 14 rigidly supported by a rod 43 extending through an aperture in wall 20 and spaced therefrom. Rod 43 is supported relative to Wall 20 by means of conductive cup 44, a ceramic cylinder 45, a metallic cylinder 46 surrounding rod 43 and sealed to gether like the sole-supporting device previously described.

As clearly shown in Figs. 1 to 3, the auxiliary electrode 15 is in the form of a thin narrow strip or band whose width and thickness relative to that of the sole is very small. This strip extends lengthwise along the central longitudinal axis of the sole and is supported by electrically insulating support rods 48 in spaced relation from recessed portion of sole 13 lest the capacitance between the auxiliary electrode and sole become unduly large. It is. also essential that the thickness of the auxiliary electrode 15 be comparatively small in order that the capacitance between edges of the electrode and the sole be kept to a minimum. An external connection to the auxiliary electrode 15 may be made by way of a support assembly 47 similar to support assembly 37 of sole 13.

In Figs. 4 and 5, the electrical circuit connections to the tube are shown. In Fig. 4 a source of unidirectional voltage 50, such as a battery, is connected between the anode 11 and sole 13 so that the anode is positive with respect to the sole. One terminal of a source 55 of modulating voltage is connected through a coupling capacitor 57 to the auxiliary or modulating electrode 15. A load resistor 58 is connected between the auxiliary electrode 15 and the sole 13 and the latter is connected to the anode through a capacitor 59 which bypasses unidirectional source 50 and serves to maintain the anode and sole at the same R. F. potential. The other terminal of modulator 55 is connected to the anode 11. The modulator 55 is thus connected between the modulating electrode 15 and the anode 11 in so far as R. F. voltages are concerned. By varying the output of modulator 55, the R. F. voltage between anode and modulator electrode 15, hence the R. F. voltage between anode and sole, may be varied. In this manner the intensity of the electric field between anode and sole is modulated and the frequency of oscillation of the tube, which is dependent upon the intensity of the electric field, is modulated at the desired rate. Since the capacitance between auxiliary electrode and anode across which the load resistor 58 in shunt with modulator 55 is connected is relatively small, the rating of the modulator is greatly reduced at the high frequencies required for modulation.

A modification of the electrical circuit of Fig. 4 is shown in Fig. 5 in which the anode 11 and one side of the modulator 55 are grounded. A first source 60 of unidirectional voltage is connected between the anode 11 and a common point 63 which may be connected to the cathode 12. A second source 61 of unidirectional voltage is connected between the sole and the common point 63. The potential at the positive terminal of source 61 is +V with respect to the common point 63 while the potential at the negative terminals of source 61 is V relative to the same reference point. The unidirectional source 61 is preferably variable in order to adjust the mean operating frequency of the oscillator.

A modification of the sole-modulating electrode assembly is shown in Fig. 6. The sole 13 of Fig. 6 contains a longitudinal aperture 65 in which auxiliary electrode 15 having approximately the same configuration is positioned. Although the aperture and associated modulating electrode in Fig. 6 are rectangular, the invention is by no means limited to this configuration. As in the modification of Figs. 1 to 3, care must be taken that a reasonable space is maintained between the edges of the auxiliary electrode and the apertured sole in order to keep down the inter-electrode capacitance. Since the auxiliary electrode is quite thin, the edgewise capacitance is usually insignificant. With this arrangement, a plurality of supporting means, such :as 47 in Fig. 1, will be required for modulating electrode 15.

By extending the aperture 65 the entire length of the sole, it is obvious that a split sole divided into two separate portions may be obtained. With this arrangement, however, supporting structures are required for both portions of the sole, as well as for the modulating electrode. Because of the increased number of mounting devices required for the split sole, the arrangement shown in Fig. 6 is preferred.

A further modification of the sole-modulating electrode assembly is shown in Fig. 7 and comprises a bare electrically conductive wire or rod 15' spaced from and insulatedly supported on sole 13 by means of electrically insulating supports 48. An electrical connection to the wire electrode 15' may be made by way of a support, such as 47 of Fig. 2.

This invention is not limited to linear tubes. The

anode, as well as the sole and auxiliary electrode may, for example, be of circular configuration.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is, accordingly, desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A traveling wave electron discharge device comprising a periodic delay structure, a first electrode spaced from and coextensive with said delay structure to form an interaction region therebetween, a second electrode positioned within said interaction space in loose coupling relationship with said structure, and means for supplying a modulation potential to said second electrode for effecting frequency modulation of said device.

2. A traveling wave electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electromagnetic wave energy being propagated, means for producing an electron beam moving along said region in energy-exchanging relationship with said wave energy, a first electrode spaced from and coextensive with said slow wave structure to form an interaction space therebetween, a second electrode positioned coextensive with said interaction space and said first electrode, and means for supplying a modulation potential to said second electrode for effecting frequency modulation of said device.

3. A traveling wave electron discharge device comprising a slow wave energy propagating structure producing in the region adjacent thereto fields of electro-,

magnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relationship with said wave energy, a first electrode spaced from and coextensive with said slow wave structure, a second electrode arranged coextensive with said slow wave structure at a distance from said structure substantially equal to the distance of said first electrode from said structure, and means for supplying a modulation voltage to said second electrode for eifecting frequency modulation of said device.

4. A traveling wave electron discharge device comprising a slow wave energy propagating structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relationship'with said wave energy, a first electrode spaced from and coextensive with said slow wave structure to form an interaction space therebetween, a second electrode whose surface area is small compared with that of said first electrode positioned substantially parallel to said first electrode, said second electrode being disposed coextensive with said interaction space, and means for supplying a modulating voltage to said second electrode for eifecting frequency modulation of said device.

5. A traveling wave electron discharge device comprising a periodic energy transmission network structure producing in the region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said'region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure, means for establishing said first electrode at a potential negative with respect to said periodic network structure, a second electrode insulatedly supported from a recessed portion of said first electrode and coextensive with said periodic network structure, and means for supplying a modulating voltage to said second electrode for effecting frequency modulation of said device.

6. A traveling wave electron discharge device comprising a periodic energy transmission network structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means forproducing an electron beam movingflalong.,saidregion'in energy exchanging relation with said' wave energy, a first electrode spaced from and coextensive with said periodic network structure, means for establishing said first electrode at a potential'negative with respectto said periodic network structure, said firstelectrode having a longitudinal aperture therein, a second electrode positioned within said aperture with its edges spaced from corresponding edges of said aperture said second electrode being coextensive with said periodic network, and means for supplying a modulating voltage to said'second electrode for effecting frequency modulation of said device.

7. A traveling wave oscillator comprising a periodicslow wave energy transmission network structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region inenergy exchanging relation with said wave energy, a first electrode positioned substantially parallel to said periodic network structure, said means for producing including means for supplying a unidirectional voltage between said periodic network structure and said first electrode for establishing an electric field tl'l'erebetween whose strength is dependent upon the magnitude of said voltage, the velocity of said electron beam being dependent upon the strength of said electric field and being a determinant of the frequency of oscillation of said oscillator, output coupling means connected to said periodic-network structure at the end away from which said electron beam is traveling for coupling energy therefrom, a second electrode disposed adjacent said first electrode and coextensive with said periodic network structure, and means for'supplying a modulating voltage between said periodic network structure and said second electrode for modifying, the strength of said electric field as a function of said modulating voltage and thereby modulating the frequency of said oscillator.

8. A traveling wave oscillator comprising a slow wave energy propagating structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relationship with said wave energy, a first electrode positioned substantially parallel to said structure to form an interaction space therebetween, said first electrode being maintained negative with respect to said structure, said means for producing including means connected between said structure' and said first electrode for establishing an electric field therebetween Whose magnitude is a determinant of the frequency of oscillation of said oscillator, output coupling means connected to said structure at the end thereof away from which said electron beam is traveling for coupling energy therefrom, a second electrode disposed coextensive with said interaction space and said first electrode, and means for supplying a modulating voltage to said second electrode for modifying the strength of said electric field as a function of said modulating voltage to modulate the frequency, of said oscillator.

9. A traveling wave oscillator comprising a periodic slow wave energy transmission network structure producirig in the region adjacent thereto fields of electromagnetic wave energy being. transmitted, means for producing an electronbeam moving along said region in. energy exchanging relation with saidwave energy, a first electrode positioned substantially parallel to said periodic network structure, said means for producingincluding means for supplying a unidirectionalvoltage between said'periodic network structure and said first electrode for establishing an electric field therebetween whose strength is dependent upon themagnitude of. said voltage, said means for prodircing'v further including means for deriving a magnetic field" perpendicular'to' said electric field, the' frequency of oscillation ofsaidoscillator being a function of the strengthof said magnetic and said electric fields, output coupling means connected to said periodic network structure atthe end away from which said electron beam is traveling. for coupling energy therefrom, a second electrode disposed adjacent said first electrode and coextensive with said periodic network structure, and means for supplying a modulating voltage to said second electrode for modifying the strength of said electric field as a function of said modulating voltage. and thereby modulating the frequency of said oscillator.

10. A traveling wave oscillator comprising a periodic slow wave energy transmission structure producing ina region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode positioned substantially parallel to said periodic network structure, said means for producing including means for supplying a unidirectional voltage between said periodic network structure and said first electrode for establishing an electric field therebetween whose strength is dependent upon the magnitude of said voltage, the frequency of oscillations produced in said device being a function of the strength of said electric field,- a-second electrode arranged coextensive with said network structure, said second electrode and said first electrode forming a capacitor whose reactance is small compared with that between said periodic network structure and said first electrode.

11. A traveling wave electron discharge device comprising a periodic energy-transmission networkstructure producing in the region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure, means for. establishing an electric field between said first electrode and said periodic network structure, a second electrode positioned adjacent said first electrode and coextensive with said network structure, and a single source of. modulating. voltage connected between said second electrode andsaid periodic network structure for efiecting frequency modulation of said device solely as a function of said voltage.

12. A traveling wave electron dischargedevice. comprising a periodic energy transmissionnetwork structure producing in the region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure, means for establishing an electric field between said first electrode and said periodic network structure, the frequency of operation of said device being dependent upon the magnitude of said electric field, a second electrode positioned adjacent said' first electrode and coextensive with said network structure, and a source of modulating voltage connected to said second electrode for varying said electric field solely as a function of said voltage. v

13'. A traveling wave electron discharge device comprising a periodic energy transmission network structure producing in the region adjacent thereto fields of electromagnetic wave energy beingtransmitted, means for producing an electronbeam moving along said region in energy exchanging relationship with said wave energy, and an electrode assembly spaced from and coextensive with said network structure to form an interaction space therebetween, said electrode assembly including two elements each electrically insulated from one another and coextensive with one another, and means for supplying a modulating voltage between one. of said elements and said network structure for elTecting frequency modulation of said device.

14. A traveling wave electron discharge device comprising a periodic energy transmission network structure producing in the region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure to form an interaction space therebetween, said first electrode having a first portion and two other portions extending from the edges of said first portion, and a second electrode insulatedly mounted from said first portion of said first electrode and coextensive with said interaction space.

15. A traveling wave electron discharge device comprising a periodic energy transmission network structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means for producing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure to form an interaction space therebetween, and a second electrode insulatedly supported electrically from a recessed portion of said first electrode and coextensive with said network structure and said interaction space.

16. A traveling wave electron discharge-device comprising a periodic energy transmission network structure producing in a region adjacent thereto fields of electromagnetic wave energy being transmitted, means for prodncing an electron beam moving along said region in energy exchanging relation with said wave energy, a first electrode spaced from and coextensive with said periodic network structure to form an interaction space therebetween, a second electrode insulatedly supported electrically from a recessed portion of said first electrode and coextensive with said network structure and said interaction space, and means for supplying a modulating voltage to said second electrode for efiecting frequency modulation of said device.

References Cited in the file of this patent UNITED STATES PATENTS 2,553,566 Ferguson May 22, 1951 2,607,904 Lerbs Aug. 19, 1952 2,633,505 Lerbs Mar. 31, 1953 2,702,370 Lerbs Feb. 15, 1955 2,723,376 Labin Nov. 8, 1955 FOREIGN PATENTS 969,653 France May 24, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,844,797 July 22, 1958 Edward C. Dench It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 51, after "strength" insert B column 3, line 30, for 'from", second occurrence, read for column 5, line 21, after "anode" insert ll line 39, for "61" read 6O Signed and sealed this 23rd day of September 1958.

(SEAL) Attest:

KARL ROBERT cL WATSON Attesting Oflicer Commissioner of Patents 

